PERT AnalysisUsingMS Project

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PERT Analysis Using MS Project

Scott Brunton, PMP MASc MBASenior Consultant

[email protected]



Critical Path Method

! Pre-cursor to PERT

! Developed By Dupont In 1957

! Novel, Yet Simplistic, Approach to Project

Network Modeling Requirements

! Based on ‘Fixed Estimates’ for Task

Durations



Program Evaluation & Review Technique

! Developed by Booz-Allen Hamilton in 1958

– Lockheed Missile Systems – Prime Contractor

! Polaris Mobile Submarine-Launched Ballistic

Missile Program – Special Projects Office Contract with US Navy

! Acknowledges ‘Randomness’ Surrounding

Task Duration Estimation



Outcome – Three-Point Estimate

! Studied Bias and Reliability of Task Duration

Estimates Collected by Variety of Methods

! Correlated Actual Durations with Estimates

and ‘Curve-fit’ Results

! Expected Duration

6)*4( c PessimistiMostLikelyOptimistic Expected

!!"



Outcome – Three-Point Estimate

! Underlying Probability Distribution

– Beta Distribution

! Expected Variance

# $%&

'()

* +"

6

2

Optimisticc PessimistiVariance



PMI PMBOK®

! Project Time Management

– Activity Duration Estimation

• Knowledge Area 6.4

! Risk Identification – Information Gathering Techniques

• Knowledge Area 11.2.2.2

There Are No Facts About The Future



Obtaining Credible Estimates

! Overcome Bias that Estimates are Optimistic

! Methods

– Expert Judgment

– Analogous Estimation

– Parametric Estimation

– Three-Point Estimation

– Reserve Analysis



Delphi Method of Estimation

! Experts Provide Estimates Anonymously

! Reduces Bias Injected by Influential

Participant

! Results are Summarized by Independent

Facilitator and Re-distributed to Panel

! After a Few Rounds, Estimates Will Converge

on Consensus Answer



Parkinson’s Law

An Activity Will Always Take

As Long As The Time Assigned To It.





Demonstration

! Single-Point Estimate

! PERT Using Native MS Project Toolbar

! PERT Using Calculated Fields



What If The Toolbar Isn’t Available?

! Use ‘ComAddinsDialog’ Command To Reveal

PERT Toolbar

! Microsoft Knowledgebase

– http://office.microsoft.com/en-

us/project/HA101636871033.aspx?pid=CH101759951033



Limitations of PERT

! Assumes Task Durations are Accurate and

Independent

! Assumes Underlying Probability Distribution Of

Estimates Can Be Represented By Beta! Does Not Account For Quality of Estimates

! Influenced by Underlying Contractual Arrangements

! Static Single-Pass Calculation Of Critical Path

Underestimates The Expected Project Duration – Neglects Effects of Near-Critical Tasks



Probabilistic Simulation of Task Durations

! Monte Carlo Simulation

– Statistical Method Using Random Sampling of

Configurable Probability Distribution Curves

– Apply Random Variation to Each Task Duration – Results Accumulate over Repeated Simulations

– Third Party Add-in

• Deltek – Risk+



References

! PMBOK® Third Edition – as referenced

! Project Management: A Systems Approach to Planning,Scheduling and Controlling, 6th Ed. – Harold Kerzner © 1998, ISBN 0-442-02551-3

! Field Guide to Project Management – David I Cleland © 1998, ISBN 0-471-29206-0

! Fundamentals of Project Management – James P Lewis © 1995, ISBN 0-8144-7835-2

! Project Management for Business & Engineering, 2nd Ed. – John M. Nicholas © 2004, ISBN 0-7506-7824-0

! Wikipedia - http://en.wikipedia.org/wiki/PERT



Questions

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PERT AnalysisUsingMS Project